The present invention relates to an electrophotographic copying machine.
As is known in copying machines of the aforesaid type, a photoconductive layer in the form of a sheet wrapped around, or of a coating deposited on, a drum or other cyclically movable part is sequentially carried through charging, exposing, developing, transfer and cleaning stations disposed adjacent the path of this movable part.
Copying machines of the aforesaid type are known which are capable of supplying copies on sheets of different formats and therefore of photocopying originals having different formats. In this case, both the lateral dimension and the longitudinal dimension of the photoconductive sheet or coating will obviously have to be at least equal to the maximum lateral and longitudinal dimensions of the copy sheets.
A first disadvantage of these types of machines may arise when it is intended to photocopy parts only of originals having a format exceeding that of the copy sheets present for the time being in the machine. In this case, during stage 4, only part of the image of the original is transferred in the form of particles of colour to the copy sheet, while the particles of colour constituting that part of the image on the photoconductive surface which exceeds the format of the copy sheet are removed during the cleaning stage.
The disadvantage consists in the fact that, if the aforesaid procedure is prolonged for many copying cycles a useless consumption of developing powder or liquid occurs for rendering visible on the photoconductive layer that part of the image of the original which exceeds the format of the copy sheet used; moreover, the cleaning device becomes overloaded, since the particles of colour to be removed are much more than those which normally remain on the photoconductive layer when the transfer of the image to the copy sheet is complete. Finally, in the case in which developing powder is used, the amount of powder circulating unduly through the machine is greatly increased, with all the drawbacks deriving from the presence of powder in the various devices of the machine.